Manufacturing methods of MEMS device

ABSTRACT

The present invention is directed to manufacturing methods of electrostatic type MEMS devices. The manufacturing method of the present invention includes the steps of forming a substrate side electrode on a substrate, forming a fluid film before or after forming a sacrificial layer, further forming a beam having a driving side electrode on a planarized surface of the fluid film, and finally, removing the sacrificial layer. Furthermore, performing the foregoing method planarizes the surface of a driving side electrode, reduces fluctuations in the shape of a beam, and improves the performance and the uniformity of the MEMS device.

TECHNICAL FIELD

The present invention relates to manufacturing methods of anelectrostatic drive type MEMS device.

BACKGROUND ART

With the advances in microscopic manufacturing technology, muchattention has been focused on so-called micro-machine (MEMS: MicroElectro Mechanical Systems, ultra-miniature electric, mechanicalcompound) devices and miniature devices in which MEMS devices areincorporated.

A MEMS device is a device that is formed on a substrate such as asilicon substrate, glass substrate or the like as a microscopicstructure, and electrically and further, mechanically unites a drivingbody outputting mechanical driving force with a semiconductor integratedcircuit or the like that controls the mechanical body. A basic featureof the MEMS device is that a mechanically structured driving body isincorporated in a part of the device, and the driving body iselectrically driven by the use of coulombic attraction force betweenelectrodes or the like.

FIGS. 11 and 12 show a typical composition of an optical MEMS devicethat is applied to an optical switch and a light modulation device bytaking advantage of the reflection or diffraction of light.

An optical MEMS device 1 shown in FIG. 11 includes a substrate 2, asubstrate side electrode 3 formed on the substrate 2, a beam 6 having adriving side electrode 4 that is disposed in parallel to oppose thesubstrate side electrode 3, and a support part 7 for supporting one endof the beam 6. The beam 6 and substrate side electrode 3 areelectrically insulated by a void 8 therebetween.

A required substrate such as a substrate with an insulation film formedon a semiconductor substrate of, for example, silicon (Si), galliumarsenic (GaAs) and the like, or an insulative substrate such as a glasssubstrate is used for the substrate 2. The substrate side electrode 3 isformed of a polycrystalline silicon film by doping impurities therein,metal film (W deposited film, for example), and the like. The beam 6 iscomposed of, for example, an insulation film 5 such as silicon nitridefilm (SiN film) or the like and the driving side film 4 serving as areflective film consisting of, for example, Al film of 100 nm or so inthickness. The beam 6 is formed in a so-called cantilever fashion withits one end supported by the support part 7.

In the optical MEMS device 1, the beam 6 displaces itself in response toelectrostatic attraction force or electrostatic repulsion forcegenerated between the substrate side electrode 3 and driving sideelectrode 4 by an electric potential applied to the substrate sideelectrode 3 and driving side electrode 4, and as shown by a solid lineas well as a broken line in FIG. 11, for example, the beam 6 displacesitself into a parallel state or inclined state relative to the substrateside electrode 3.

An optical MEMS device 11 shown in FIG. 12 is composed of a substrate12, a substrate side electrode 13 formed on the substrate 12 and a beam14 that straddles the substrate side electrode 13 in a bridge-likefashion. The beam 14 and substrate side electrode 13 are insulated by avoid 10 therebetween.

The beam 14 is composed of a bridge member 15 of, for example, a SiNfilm that rises up from the substrate 12 and straddles a substrate sideelectrode 13 in a bridge-like fashion and a driving side electrode 16of, for example, an Al film of 100 nm or so in thickness, that, servingas a refection film, is provided on the bridge member 15 to oppose thesubstrate side electrode 13 in parallel to each other. The substrate 12,substrate side electrode 13, beam 14 and the like may employ similarcompositions and materials to those explained in FIG. 11. The beam 14 isformed in a so-called bridge-like fashion in which the both ends thereofare supported.

In the optical MEMS device 11, the beam 14 displaces itself in responseto electrostatic attraction force or electrostatic repulsion forcegenerated between the substrate side electrode 13 and driving sideelectrode 16 by an electric potential that is applied to the substrateside electrode 13 and driving side electrode 16, and as shown by a solidline and a broken line as well in FIG. 12, for example, the beam 14displaces itself into a parallel state or fallen state relative to thesubstrate side electrode 13.

With these optical MEMS devices 1, 11, light is irradiated on thesurfaces of the driving side electrodes 4, 16 serving as a lightreflective film, and by taking advantage of differences in the directionof reflected light depending on positions into which the beam 6, 14 aredriven, these MEMS devices can be applied to an optical switch having aswitch function by detecting the reflected light of one direction.

Further, the optical MEMS devices 1, 11 are applicable as a lightmodulation device for modulating the strength of light. When lightreflection is taken advantage of, the strength of light is modulated byvibrating the beams 6, 14 according to the amount of reflected light ofone direction per unit time. This light modulation device runs on aso-called time modulation.

When light diffraction is taken advantage of, a light modulation deviceis composed of a plurality of beams 6, 14 disposed in parallel relativeto the common substrate side electrodes 3, 13, and by varying the heightof, for example, driving side electrodes serving as a light reflectivefilm with the movements of every other beam 6, 14 such as moving closerto or moving away from the common substrate side electrodes 3, 13, thestrength of reflected light from the driving side electrodes ismodulated by means of light diffraction. This light modulation deviceruns on a so-called space modulation.

FIG. 13 shows a composition of the GLV (Grating Light Valve) devicedeveloped by SLM (Silicon Light Machines) as a light strength modulationdevice for a laser display, that is, light modulator.

In a GLV device 21, as shown in FIG. 13A, a common substrate sideelectrode 23 of a refractory metal, for example, a tungsten thin film ora nitride film thereof, or of a poly-crystalline silicon thin film isformed on an insulation substrate 22 such as a glass substrate 22 or thelike, and a plurality of beams 24, in this example, six beams [24 ₁, 24₂, 24 ₃, 24 ₄, 24 ₅, 24 ₆] straddling across the substrate sideelectrodes 23 in a bridge-like fashion are disposed in parallel. Thecompositions of the substrate side electrode 23 and beams 24 are thesame as those explained in FIG. 11. Namely, as shown in FIG. 13B, areflective film cum driving side electrode 26 of an Al film of 100 nm orso in thickness is formed on the surface, which is in parallel to thesubstrate side electrode 23, of a bridge member 25 of a SiN film, forexample.

The beam 24 composed of the bridge member 25 and reflective film cumdriving side electrode 26 provided thereon is a portion conventionallycalled a ribbon.

The aluminum film (Al film) used as the reflective film cum driving sideelectrode 26 is a suitable metal as the material for optical componentsbecause of the following reasons: (1) it is a metal that can becomparatively easily formed into a film; (2) the dispersion ofreflectance with respect to wavelengths in a visible light range issmall; (3) alumina natural oxidation film generated on the surface ofthe Al film functions as a protective film to protect a reflectivesurface.

Further, the SiN film (silicon nitride film) composing the bridge member25 is formed by the use of the low-pressure CVD method, and the SiN filmis selected by reason of the physical values of its strength, elasticityconstant, and the like being suitable for mechanically driving thebridge member 25.

When a small voltage is applied between the substrate side electrode 23and reflective film cum driving side electrode 26, the above-mentionedbeam 24 moves closer to the substrate side electrode 23 according to theabove-mentioned electrostatic phenomenon, and when the application ofthe voltage is stopped, the beam 24 moves away from the substrate sideelectrode 23 and returns to an original position.

The GLV device 21 alternately varies the height of the reflective filmcum driving side electrode 26 with the movements of the plurality ofbeams 24 such as moving closer to or moving away from the substrate sideelectrode 23 (that is, those movements of every other beams), andmodulates the strength of light reflected on the driving side electrode26 by means of the diffraction of light (one beam spot is irradiated onthe whole of six beams 24).

Mechanical characteristics of the beam driven by taking advantage ofelectrostatic attraction force and electrostatic repulsion force arealmost predicated on the physical properties of the SiN film formed bythe use of the CVD method or the like, with an Al film mainlyfunctioning as a mirror.

By the way, as described above, the substrate side electrode in the MEMSdevice is formed on an insulation layer of a semiconductor substratemade of silicon, GaAs, or the like, or an insulative substrate such as aglass substrate. As for materials of the electrode, a polycrystallinesilicon film or metal film, in which impurities are doped is used.However, since these materials have a crystalline structure, thereoccurs unevenness on the surface thereof. For example, in the case of apolycrystalline silicon electrode, according to an analysis by AFM (anatomic force microscope), controlling relative roughness RMS (root meansquare) value of a surface can be achieved by strictly carrying outtemperature control in the manufacturing process, and it is a well knownfact that there easily occurs surface relative roughness of 20 nm ormore after a conventional film forming process and a semiconductormanufacturing process that have so far been practiced. The degree of theroughness depends on materials and film forming methods as well.

This surface unevenness poses not so serious a problem in terms of theelectric characteristics as well as the operating characteristics of theMEMS device, though it often has become problems in the manufacturingprocess of an optical MEMS device. Namely, the substrate side electrodeof the above-mentioned MEMS device is usually positioned under thereflective film cum driving side electrode. In this case, surfaceunevenness of a lower layer film becomes sequentially transcribed to anupper layer film in the manufacturing process, thereby resulting in theforming of a driving side electrode with piled-up transcribed surfaceunevenness, that is, the forming of a reflective film therewith on theuppermost layer that is an optically important film surface.

As one of the manufacturing methods of the MEMS device, there is amethod in which a multi-layer structure is formed by repeatedlylaminating and processing thin films, and thereafter by selectivelyremoving one layer of the multi-layer structure to manufacture aso-called hollow structure that has a void between a substrate sideelectrode and beam. This manufacturing method is shown in FIGS. 14A to14D. This example is the case of being applied to manufacturing theabove-mentioned MEMS device 1 shown in FIG. 11.

First, as shown in FIG. 14A, the substrate side electrode 3 of, forexample, a polycrystalline silicon film is formed on a substrate 2 inwhich an insulation film 10 such as SiO₂ film or the like is formed onthe upper surface of, for example, a silicon substrate 9, and afterforming a support part 7, a sacrificial layer 18 for forming a void isformed on a surface including the substrate side electrode 3. Next, asshown in FIG. 14B, for example, a silicon nitride (SiN) film 5 and adriving side electrode material layer of, for example, an aluminum (Al)film 4′ constituting a beam are formed on the support part 7 andsacrificial layer 18. Next, as shown in FIG. 14C, the silicon nitridefilm 5 and aluminum film 4′ are subjected to patterning through a resistmask 19 to thereby form a beam 6 composed of the silicon nitride film 5and a driving side electrode 4 made of aluminum. Thereafter, as shown inFIG. 14D, by removing the sacrificial layer 18 to form a void 8 betweenthe substrate side electrode 3 and beam 6, the MEMS device 1 ismanufactured.

Silicon (for example, non-crystalline silicon, polycrystalline silicon,or the like) or a silicon oxide film is used to form the sacrificiallayer 18. When the sacrificial layer 18 is made of silicon, it can beremoved by, for example, a mixture of nitric acid and fluoric acid, orby gas etching employing gas which contains fluorine (F) And when thesacrificial layer 18 is made of an oxidized layer, it is conventionallyremoved by an oxygen fluoride solution, or by plasma etching employingfluorinated carbon gas.

With such optical MEMS device as manufactured to have a three-layerstructure of a substrate side electrode (a) a sacrificial layer (b) forforming a void, and a reflective film cum driving side electrode (c),assuming that the maximum values of surface unevenness that are observedin each of the respective layers are R_(max) (a), R_(max) (b), R_(max)(c), there is a possibility that when the three layers are laminated,the amount of surface unevenness on the surface of the uppermost layeradds up to the sum of these maximum values.

Describing the performance of optical components of the MEMS device inwhich aluminum (Al) is made to serve as a reflective film, 92% of thereflectance of the Al film may possibly be obtained if the film is abulk Al film. However, if there is no controlling on the amount of thissurface unevenness, the reflectance will deteriorate by more thanseveral percentage points, so that only 85% or so thereof can barely beobtained. In an extreme case, it is observed that the surface appears tobe clouded up. With such an optical MEMS device, as shown in FIG. 15,(an enlarged view of the relevant part of a driving portion), forexample, when the substrate side electrode 3 is formed ofpolycrystalline silicon, unevenness on the surface of thepolycrystalline silicon film increases and is transcribed onto thesurface of the driving side electrode (Al film) 4 composing the beam (anAl/SiN laminated film) 6, resulting in the deterioration of lightreflectance of the driving side electrode serving as a mirror.

Further, there remains a design problem. A MEMS transducer, that is, theresonant frequency of a beam is usually designed by taking account ofthe mass of resonance, the tensile force of films in respective regionsthat support the driving part and the like, though in the presentcircumstances at a time of designing the values of physicality of therespective films are conventionally computed and designed by using thevalues of physicality on the assumption that those films are in an idealthin state. Then, as shown in FIG. 16, for example, in case there existsa semi-sphere of 0.3 μm in the substrate side electrode 3, when thesacrificial layer 18 of 0.5 μm is formed on the substrate side electrode3, there is formed a semi-sphere b of 1.3 μm in diameter by isotropicfilm forming; and when the beam 6 is formed thereupon, the surfaceunevenness of the beam 6 further increases.

When the beam is sufficiently thick in comparison with this 1.3 μm, theunevenness is observed as that inherent in the beam 6. However, when thefilm thickness of the beam becomes thinner, the own shape of the beam 6is transformed, and the beam 6 is observed to have, for example, afolded structure (referring to FIG. 17). At this time, there occurs theproblem that the MEMS device is unable to have dynamic characteristicsin accordance with design. FIG. 18 shows an example thereof. In the casewhere the tensile force of the beam 6 is taken advantage of to drive theMEMS device, if the beam 6 having the film shape is pulled by both endsusing the tensile force, its accordion structure stretches out,resulting in wild fluctuations of the physicality value that isapproximated by a spring.

As explained above, the surface unevenness of the substrate sideelectrode has not only affected the relative roughness of the surface ofthe beam, but also been a factor in the fluctuations of parametersinherent in the MEMS device such as resonance frequency and the like.

DISCLOSURE OF THE INVENTION

The present invention provides a manufacturing method of a MEMS device,in which the surface of a beam is made to be planarized, fluctuations inthe shape of the beam is reduced, thereby improving the performance anduniformity in the performance as well.

A manufacturing method of a MEMS device according to the presentinvention has the steps of: forming a substrate side electrode on asubstrate, forming a fluid film on the substrate side electrode, forminga sacrificial layer on a planarized surface of the fluid film, formingon the sacrificial layer a beam having a driving side electrode, andremoving the sacrificial layer.

A manufacturing method of a MEMS device according to the presentinvention has the steps of: forming a substrate side electrode on asubstrate, forming a sacrificial layer on the substrate side electrodethrough a protective film, or not through the protective film, forming afluid film on the sacrificial layer, forming a beam having a drivingside electrode on a planarized surface of the fluid film, and removingthe sacrificial layer.

As the fluid film mentioned above, a silicate glass film whose coveringform of a step is fluid form can be employed. The silicate glass film isformed of phosphor, boron, or formed containing the both, and afterforming the silicate glass film, heat treatment is applied thereto, andthe surface of the above-mentioned silicate glass can be planarized.

The silicate glass film is formed of a silicon oxide film by means ofthe CVD method wherein ozone and alkoxysilane are used as materials.

According to a manufacturing method of a MEMS device of the presentinvention, since a substrate side electrode is formed on a substrate,and then a fluid film is formed on the substrate side electrode,followed by sequentially forming a sacrificial layer and a beam on theplanarized surface of the fluid film, the surface of the beam becomesplanarized without unevenness. Since the sacrificial layer is removedthereafter, the beam having a driving side electrode with the planarizedsurface can be formed with a required void against the substrate sideelectrode.

Further, according to another manufacturing method of a MEMS device ofthe present invention, since a substrate side electrode is formed on asubstrate, and then a sacrificial layer is formed on the substrate sideelectrode through a protective film or not through the protective film,followed by forming a fluid film on the sacrificial layer to form a beamon the planarized surface of the fluid film, the surface of the beambecomes planarized without unevenness. Since the sacrificial layer isremoved thereafter, the beam having a driving side electrode with theplanarized surface can be formed with a required void against thesubstrate side electrode.

According to the above-mentioned manufacturing method of the MEMS deviceof the present invention, since a fluid film is formed before or after asacrificial layer is formed, followed by forming an insulation film anddriving side electrode composing a beam on the planarized film by thefluidization of the fluid film, the surface of which is ultimatelyplanarized can be formed. Therefore, uniformity of the film composingthe beam is obtained to reduce the fluctuations in the shape of thefilm, and the physicality value of the beam is not largely fluctuated.In addition, since unevenness on the surface of the beam can beplanarized and fluctuations in the vibratory characteristics of the beamcan be reduced as well, uniformity in the performance of the MEMS devicecan be improved and the high-quality MEMS device can be manufactured ona large scale. When the MEMS device which is manufactured according tothe manufacturing method of the present invention is applied to anoptical MEMS device that is used for, for example, an optical switch ora light modulation device and the like using the light reflectance orlight diffraction, the light reflectance of the driving side electrodeserving as a light reflective film improves, and light use efficiency asan optical MEMS device can be improved as well.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1C are diagrams of a manufacturing process (first sequence)showing one embodiment of a manufacturing method of one typicalelectrostatic drive type MEMS device according to the present invention;

FIG. 2A to 2C are diagrams of a manufacturing process (second sequence)showing one embodiment of the manufacturing method of one typicalelectrostatic drive type MEMS device according to the present invention;

FIG. 3A is an enlarged cross-sectional view of a relevant part of FIG.2A, and FIG. 3B is an enlarged cross-sectional view of a relevant partof FIG. 2C;

FIG. 4A to 4C are diagrams of a manufacturing process (first sequence)showing another embodiment of a manufacturing method of one typicalelectrostatic drive type MEMS device according to the present invention;

FIG. 5A to 5B are diagrams of a manufacturing process (second sequence)showing another embodiment of the manufacturing method of one typicalelectrostatic drive type MEMS device according to the present invention;

FIG. 6A to 6C are diagrams of a manufacturing process (first sequence)showing further another embodiment of a manufacturing method of onetypical electrostatic drive type MEMS device according to the presentinvention;

FIGS. 7A and 7B are diagrams of a manufacturing process (secondsequence) showing further another embodiment of the manufacturing methodof one typical electrostatic drive type MEMS device according to thepresent invention;

FIG. 8A is an enlarged cross-sectional view of a relevant part of FIG.4C, and FIG. 8B is an enlarged cross-sectional view of a relevant partof FIG. 5B;

FIG. 9A is a diagram showing a layout of a mask which is applied when afluid film of the present invention is formed, and FIG. 9B is across-sectional view thereof;

FIG. 10A to 10D are diagrams of a manufacturing process showing oneembodiment of a manufacturing method of another typical electrostaticdrive type MEMS device according to the present invention;

FIG. 11 is a typical example of an optical MEMS device for explaining aconventional one;

FIG. 12 is another typical example of the optical MEMS device forexplaining a conventional one;

FIG. 13A is a structural diagram showing a conventional GLV device, andFIG. 13B is a cross-sectional view thereof;

FIG. 14A to 14D are diagrams of a manufacturing process showing amanufacturing method of a conventional electrostatic drive type MEMSdevice;

FIG. 15 is a cross-sectional view of a relevant part of a conventionaloptical MEMS device, showing the unevenness of a driving side electrodethereof;

FIG. 16 is an explanatory diagram of a state in which the unevenness ofunderlaid layer is expanded and transcribed to an upper layer;

FIG. 17 is a cross-sectional diagram showing the shape of a filmconstituting a beam obtained by a conventional manufacturing method; and

FIG. 18 is a cross-sectional diagram showing the shape of a filmconstituting a beam obtained by the conventional manufacturing method.

BEST MODES FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be explained withreference to drawings.

FIGS. 1 to 3 show one embodiment of a manufacturing method of a MEMSdevice according to the present invention. This embodiment is the casein which the present invention is applied to manufacturing a typicalelectrostatic drive type MEMS device.

First, as shown in FIG. 1A, a substrate side electrode 34 is formed on asubstrate, in this embodiment, a substrate 31 in which an insulationfilm 33 is formed on a semiconductor substrate 32. The semiconductorsubstrate 32 can be formed of, for example, a silicon (Si) substrate,gallium arsenic (GaAs) substrate or the like, and the insulation film 33can be formed of a silicon oxide (SiO₂) film, silicon nitride (SiN) filmor the like. The substrate side electrode 34 can be formed of apolycrystalline silicon film, metal film or the like, into whichimpurities are doped, and in this embodiment, formed of animpurities-doped polycrystalline silicon film. A surface 34 a of thesubstrate side electrode 34 formed of the polycrystalline silicon filmhas, as shown in FIG. 3A, considerable unevenness.

Next, as shown in FIG. 1B, a fluid film 35, the surface of which isplanarized by fluidization, is formed on the overall surface includingthe surface of the substrate side 34.

This fluid film 35 can be formed in the following manner.

As the fluid film 35, for example, a phosphor-doped or boron-doped, orthe both-doped (phosphor and boron) silicon oxide film, so-called PSG(phosphor silicate glass), BSG (boron silicate glass), or PBSG (phosphorboron silicate glass) film is formed by the CVD (Chemical VaporDeposition) method. Concentrations of the phosphor and boron to be dopedcan respectively be made approximately 7% by weight, and theabove-mentioned silicate glass film doped with either of them or both ofthem can be used. After the fluid film 35 composed of theimpurities-doped silicate glass is formed, anneal treatment at 750° C.or more is performed to fluidize the fluid film 35, and the surfacethereof is planarized. The CVD method is carried out employing chemicalvapor deposition of a hot wall type in which a silane gas 50 cc/Min. andN₂O gas 100 cc/Min. are used as reactive gas. PH₃ is used as a materialfor doping phosphor, and B₂H₆ is used as a material for doping boron.The anneal treatment can be carried out in the atmosphere of, forexample, a nitride gas at 850° C. for thirty minutes.

As for another embodiment, a silicate glass film constituting the fluidfilm 35 can be formed of a silicon oxide film by the CVD method in whichozone and alkoxysilane are used as materials. For example, the siliconoxide film is formed by the normal-pressure CVD method in which, forexample, TEOS (tetraethoxysilane) and ozone are used as materials. Asthe conditions for forming a film, the quantity of flow of TEOS is setto approximately 40 cc/min. and that of ozone is set to approximately350 cc/min.; oxygen and diluted nitride are used to transport the ozone;and the substrate temperature is set at about 350° C. With the CVDmethod in which TEOS and ozone are used as materials, a film is formedas fluidization is being maintained, and when the fluid film 35 isformed, the surface thereof has been already planarized. This silicateglass film can be formed of either a non-doped film or animpurities-doped film (for example, BSG film, PSG film). As acharacteristic of the CVD using TEOS/ozone, it is noted that a similarfluid form to those of the above-mentioned BSG film, PSG film and BPSGfilm is obtained when a step on the substrate are covered thereby. Inthis embodiment, a formed non-doped dioxide silicon film also planarizesunevenness on the surface of the substrate side electrode 23 to providean extremely planarized and smooth surface. In terms of otherphysicality and film characteristics, there is no obvious differencebetween the above-mentioned impurities-doped silicate film and ozoneTEOS CVD oxide film, and a required MEMS device to be mentioned later oncan be obtained by either of the manufacturing method. Although TEOS isused in this embodiment, other alkoxysilane such as tetramethoxysilane,tetraisopropoxysilane, and the like may be used. Meanwhile, since itbecomes difficult to obtain a fluid form as the number of carbons ofalkoxysilane increases, a thicker film is needed in order to obtain arequired surface smoothness. Further, material including fluorine suchas triethoxysilane fluoride [(C₂H₅O) 3CF] and the like may be used. Inthat case, a similar result is also obtained, and further, since aformed film includes fluorine, there occurs added value that enables lowdielectric constant film to be obtained, thereby contributing toimproving the characteristic of the MEMS device.

Next, as shown in FIG. 1C, an insulation film that becomes a supportpart, such as a silicon nitride (SiN) film, silicon oxide (SiO₂) filmand the like, in this embodiment, silicon nitride film is formed on thesurface of the fluid film 35 by the CVD method or the like, andpatterning is applied thereto to form a support part 36 of the siliconnitride film at a position detached from the substrate side electrode34.

Next, as shown in FIG. 2A, a sacrificial layer 37 for forming a void, inthis embodiment, non-crystalline silicon layer is formed over theoverall surface of the fluid layer 35, followed by etching thenon-crystalline silicon layer 37 so that the surface becomes flush withthe surface of the support part 36. Further, as the sacrificial layer37, other than a non-crystalline film, polycrystalline silicon film,photoresist film or insulating film (for example, silicon oxide film,silicon nitride film) and the like that are different in etching ratefrom an insulation film that composes the support part 36 and a beam asdescribed later on can be used. For the purpose of improving theperformance of the MEMS device, however, it is necessary to carefullyselect the kind of film while controlling the growth in diameter ofgrains of the film itself used as a sacrificial layer, otherwise theeffectiveness of the lower electrode/fluid film whose surfaces have beenplanarized may disappear.

Next, an insulation film of, for example, silicon nitride film, siliconoxide film or the like, in this embodiment, silicon nitride film 38 isformed on the overall surface including the surface of the support part36 and that of the non-crystalline silicon layer 37 serving as asacrificial layer, followed by forming thereupon a driving sideelectrode material layer 39′ of, in this embodiment, an Al materiallayer. FIG. 3A shows enlarged relevant part thereof. As the driving sideelectrode material layer, a silver Ag film, an Al film mainly consistingof aluminum (Al) as components, a refractory metal film formed of suchas titanium Ti, tungsten W, molybdenum Mo, tantalum Ta, or the like canbe used.

Next, as shown in FIG. 2B, a resist mask 40 is formed, and a drivingside electrode material layer 39′ and silicon nitride film thereunderare selectively removed by etching through the resist mask 40 so as toform a beam 41 composed of a driving side electrode (Al electrode) 39and silicon nitride film 38, which is supported by the support part 36.

Next, as shown in FIG. 2C, the non-crystalline silicon film 37constituting a sacrificial layer is removed by gas etching with, forexample, XeF₂ gas to form a void 42 between the substrate side electrode34 (substantially, fluid film 35) and beam 41, and as a result, atargeted electrostatic drive type MEMS device 43 having a structure of acantilever fashion can be obtained. FIG. 3B shows an enlarged relevantpart thereof including the beam 41.

This MEMS device 43 is such composed as to have the fluid film 35, whichhas a planarized surface and serves as a protective film, on theconsiderably uneven surface of the substrate side electrode 34, and tohave the beam 41 that is detached from the fluid film 35 with therequired void 42 therebetween and has a planarized surface and aplanarized reverse surface opposing the fluid film.

According to the manufacturing method of this embodiment, after formingthe substrate side electrode 34 of polycrystalline silicon, the fluidfilm 35 is formed; and the sacrificial layer 37, silicon nitride film 38and driving side electrode material layer 39′ that compose a beam aresequentially formed on the fluid layer 35 with its surface 35 a havingbeen planarized, so that the surfaces of the sacrificial layer 37, thesilicon nitride film 38, and the driving side electrode material layer39′ are planarized, and as a result, the beam 41 with its surfaceultimately being planarized can be formed. Namely, when the driving sideelectrode 39 is formed of an Al film, for example, the surface of the Alfilm reflects only the unevenness of crystallized grains of the Al film.Consequently, as shown in 3B, the beam 41 having favorable flatness canbe formed.

Therefore, the uniformity of the film of the beam 41 can be obtained,the fluctuations in the film shape of the beam can be reduced, and thereare no considerable fluctuations in the physicality value of the beam,with the result that it is possible to obtain the MEMS device, in whichthe whole film of the beam is without any fluctuation.

Further, since it is possible to get rid of the unevenness of thesurface of the beam 41 and reduce the fluctuations in the number ofvibration and the like of the beam 41, uniformity in the performance ofthe MEMS device can be improved, and the mass-production of thehigh-quality MEMS device 43 is made possible.

When the MEMS device 43 manufactured according to the embodiment isapplied to the optical MEMS devices used in, for example, an opticalswitch, a light modulation device or the like that takes advantage oflight reflection or light diffraction, light reflectance on the drivingside electrode 39 serving as a light reflective film can be improved,and the improvement of light use efficiency as the optical MEMS devicecan be implemented.

While in the above-mentioned embodiment the support part 36 is formed bypatterning, further with respect to a method of forming this supportpart, another embodiment will be described. FIGS. 4 and 5 show anotherembodiment of the manufacturing method of the MEMS device according tothe present invention.

First, the same as in FIG. 1B, as shown in 4A, the patterned substrateside electrode 34 is formed on the substrate 31 consisting of theinsulation film 33 formed on the semiconductor substrate 32, forexample, and the fluid film 35 is formed on the substrate side electrode34. Next, for example, the non-crystalline silicon film 50 serving asthe sacrificial layer is formed on the overall surface of the planarizedsubstrate.

Next, as shown in FIG. 4B, an opening 51 is formed at a predeterminedposition of the non-crystalline silicon film 50, that is, at a portioncorresponding to a support part (columnar support: post) for supportingthe beam which is formed later on.

Next, as shown in FIG. 4C, an Al/SiN laminated film consisting of theinsulation film (for example, silicon nitride film) 38 and driving sideelectrode material layer (for example, Al material) 39′ is formed overthe non-crystalline silicon film 50 including the inside of the opening51. Here, the AL/SiN laminated film formed on the side walls of theopening 51 becomes a support part 52 for supporting the beam, that is, apost of cylinder or square column in shape with its core hollowing out.

Next, as shown in FIG. 5A, by patterning the Al/SiN laminated filmcomposed of the silicon nitride film 38 and non-crystalline film 39′,there is formed the beam 41 composed of the silicon nitride 38 anddriving side electrode 39 thereupon. Next, the non-crystalline filmconstituting a sacrificial layer is removed to obtain the targeted MEMSdevice 44, as shown in FIG. 5B. In FIG. 5B, since the beam 41 iselongated in one direction from the support part 52, the MEMS device ina so-called cantilever fashion can be obtained.

As with this embodiment, similar effectiveness to those of theabove-mentioned manufacturing method shown in FIGS. 1 to 3 can beobtained. Further, the MEMS device 44 manufactured according to thisembodiment is favorably applied to the optical MEMS device used for, forexample, the optical switch, light modulation device and the like as isthe above-mentioned MEMS device 43.

FIGS. 6 to 8 show another embodiment of the manufacturing method of theMEMS device according to the present invention. This embodiment is alsoa method that is applied to manufacturing the typical electrostaticdrive type MEMS device with its beam in the same cantilever fashion asmentioned above.

First, as shown in FIG. 6A, the substrate side electrode 34 is formed ona substrate, in this embodiment, the substrate 31 consisting of theinsulation film 33 such as silicon oxide (SiO₂) film formed on thesilicon semiconductor substrate 32. The substrate side electrode 34 canbe formed of polycrystalline silicon film, metal film or the like, intowhich impurities are doped, and in this embodiment, the impurities-dopedpolycrystalline film is employed. As shown in FIG. 8A, a surface 34 a ofthe substrate side electrode 34 of the polycrystalline silicon film hasconsiderable unevenness.

Next, as shown in FIG. 6B, after forming a protective film, in thisembodiment, silicon oxide (SiO₂) film 46 on the surface of the substrateside electrode 34, an insulation film serving as a support part, such asa silicon nitride (SiN) film, silicon oxide (SiO₂) film, or the like, inthis embodiment, silicon nitride film is formed by the CVD method or thelike, followed by patterning the silicon nitride film to form thesupport part 36 of the silicon nitride film at a position detached fromthe substrate side electrode 34.

Next, a sacrificial layer 37 for forming a void, in this embodiment,polycrystalline silicon layer is formed, followed by etching thepolycrystalline silicon layer 37 to become flush with the support part36. Meanwhile, as the sacrificial layer 37, similarly to the embodimentsmentioned above, other than a polycrystalline film, a non-crystallinesilicon film, photoresist film, insulation film (for example, siliconoxide film, silicon nitride film or the like) that is different inetching rate from an insulation film constituting the support part 36and a beam mentioned later on, or the like can be used.

Next, as shown in FIG. 6C, the fluid film 35 with its surface planarizedby the same fluidization as mentioned above is formed on the overallsurface including the surface of the support part 36 and thepolycrystalline silicon layer 37 constituting sacrificial layer. Asmentioned above, this fluid layer 35 is formed by using the method inwhich after an impurities-doped silicate glass film (for example, BSGfilm, PSG film, PBSG or the like) is formed, anneal treatment is appliedthereto, or formed of a silicon film manufactured by the CVD method inwhich ozone and alkoxysilane are used as materials.

An insulation film such as, for example, silicon nitride film, siliconoxide film or the like, in this embodiment, the silicon nitride film 38is formed on the fluid film 35, and further the driving side electrodematerial layer 39′, in this embodiment, Al material layer is formedthereupon. FIG. 8A shows an enlarged relevant part thereof. As drivingside electrode material layer, the same as was mentioned above, an Agfilm, Al film mainly consisting of aluminum (Al) as components, orrefractory metal film of such as titanium Ti, tungsten W, molybdenum Mo,tantalum Ta, or the like can be used.

Next, as shown in FIG. 7A, the resist mask 40 is formed, and the drivingside electrode material layer 39′, and silicon oxide film 38, fluid film35 thereunder are selectively removed by etching through this resistmask 40 to form the beam 41 composed of the driving side electrode (ALelectrode) 39 and silicon nitride film 38, which is supported by thesupport part 36. In this embodiment, since the fluid film 35 remains,the beam 41 is formed of a three-layer film of the driving sideelectrode 39, silicon nitride film 38 and fluid film 35.

Next, as shown in FIG. 7B, the polycrystalline silicon layer 37constituting a sacrificial layer is removed. When the sacrificial layer37 is formed of polycrystalline silicon, it can be easily removed byetching with XeF₂ gas, as mentioned above. The void 42 is formed betweenthe substrate side electrode 34 (substantially, protective film 46) andbeam 41 by removing the sacrificial layer 37 to obtain the targetedelectrostatic drive type MEMS device 47 in which the beam is structuredin a cantilever fashion. FIG. 8B shows an enlarged relevant part thereofincluding the beam 41.

This MEMS device 47 is structured to have the beam 41 which has theplanarized surface and planarized reverse surface opposing the fluidfilm, and is detached from the considerably uneven substrate sideelectrode 34 (substantially, protective film 46), with the required void42 therebetween.

The film stress of the fluid layer 35 formed of silicate glass issufficiently small compared with the silicon nitride film, so that thefluid film 35 on the undersurface of the beam 41 can remain, as is inthis embodiment, depending on the state of use. In another case, it ispossible to form the beam 41 having a two-layer film of the driving sideelectrode 39 and silicon nitride film 38 by removing the fluid film 35using a dilute solution of fluorine oxide, followed by supercriticaldehydration.

In the above embodiment, since the substrate side electrode 34 is formedof polycrystalline silicon and the sacrificial layer 37 is formed ofsilicon, a protective layer 46 serving as an etching stopper is formedon the surface of the substrate side electrode 34, though it is possibleto omit this protective layer 46 depending on the material of thesacrificial layer 37.

Here, a conceptual diagram is shown in which the unevenness of theundersurface of the fluid film 35 opposing the substrate side electrode34 conforms to that of the surface of the insulation film 46 formed onthe substrate side electrode 34, because the non-crystalline siliconcapable of accurately transcribing underlay unevenness is used assacrificial layer thin material. However, when polycrystalline silicon,for example, is used as the sacrificial layer thin material, since thereoccurs grain diameter distribution, the undersurface of the fluid layer35 may have considerable unevenness.

According to the manufacturing method of the MEMS device of theembodiment, since the fluid layer 35 is formed after the substrate sideelectrode 34 of polycrystalline silicon, protective film 46, andsacrificial layer 37 are formed, and then on the planarized surface 35 aof the fluid layer 35 the silicon nitride film 38 and driving sideelectrode material layer 39′ composing the beam are sequentially formed,the surface of the silicon nitride film 38 and the surface of thedriving side electrode material layer 39′ are planarized, with theresult that the beam 41, the surface of which is planarized, can beobtained.

Therefore, the uniformity of the film of the beam 41 can be obtained toreduce fluctuations in the film shape of the beam, and there are noconsiderable fluctuations in the physicality value of the beam, with theresult that it is possible to obtain the MEMS device in which the wholefilm of the beam is without any fluctuation. Further, since it ispossible to get rid of the unevenness of the surface of the beam 41 andto reduce the fluctuations in the number of vibrations and the like ofthe beam 41, the uniformity in the performance of the MEMS device can beimproved, and the mass-production of the high-quality MEMS device 43 ismade possible.

When the MEMS device 47 manufactured according to the embodiment isapplied to the optical MEMS device used in, for example, an opticalswitch, light modulation device or the like, which takes advantage oflight reflection or light diffraction, light reflectance on the drivingside electrode 39 serving as a light reflective film can be improved andthe improvement of light use efficiency as the optical MEMS device canbe implemented.

The fluid film 35 is at least required to be formed only under theportion corresponding to the beam 41. Therefore, as shown in FIGS. 9Aand 9B, in order to form the fluid layer 35 at the portion correspondingto the beam 41 including the upper part of the substrate side electrode34, the resist mask 51 is formed. A part 52 is an opening. Using thisresist pattern, the cross-sectional structure shown in FIG. 9B can beobtained by etching the fluid film 35 to cover the substrate sideelectrode 34. Thus, the beam 41 having the driving side electrode 39with a planarized surface can be obtained.

The above-mentioned embodiment has been applied to manufacturing theMEMS device in which the beam is of a cantilever type, though it can beapplied to manufacturing another MEMS device in which the beam is of abridge type as shown in FIG. 12.

FIGS. 10A to 10D are the case in which a manufacturing method of thepresent invention is applied to manufacturing a MEMS device of adouble-cantilever type. This embodiment is the case in which theprocesses of FIGS. 1 and 2 are applied to manufacturing the MEMS device.

First, as shown in FIG. 10A, the substrate side electrode 34 of, forexample, polycrystalline silicon is formed on a substrate, in thisembodiment, the substrate 31 consisting of the insulation film 33 formedon the semiconductor substrate 32. Next, the fluid film 35 with itssurface planarized by the above-mentioned same fluidization is formed onthe substrate 31 including the substrate side electrode 34.

Next, as shown in FIG. 10B, the sacrificial layer 37 for forming a voidis selectively formed on the planarized fluid film 35 at a positioncorresponding to the position of the substrate side electrode 34.

Next, as shown in FIG. 10C, an insulation film of, for example, thesilicon nitride film 38 and the driving side electrode material 39′ of,for example, an Al film are sequentially formed on the sacrificial layer37 including over the planarized fluid film 35, and a beam 54 of thedouble-cantilever type consisting of the driving side electrode 36 andsilicon nitride film 38 serving thereunder as a bridge is formed bypatterning.

Next, as shown in FIG. 10D, the sacrificial layer 37 is removed to forma void 55 between the substrate side electrode (substantially, fluidfilm) 34 and beam 54, with the result that a targeted electrostaticdrive type MEMS device in which the beam is formed in a bridge-likefashion can be obtained.

Further, though not shown in the figures, the MEMS device of thedouble-cantilever type can be manufactured by using the processes ofFIGS. 6 and 7.

As with the manufacturing method shown in FIG. 10, similar effectivenessto those of the above-mentioned embodiments can be obtained.

The manufacturing method of the present invention can be applied tomanufacturing the above-mentioned GLV device 21, though not shown in thefigures.

1. A manufacturing method of a MEMS device, comprising the steps of: forming a substrate side electrode on a substrate; forming a fluid film on said substrate and said substrate side electrode; forming a support member detached from said substrate side electrode on said fluid film; forming a sacrificial layer on said fluid film so that said sacrificial layer and said support member form a continuous surface; forming an insulating layer on said continuous surface; forming a driving side electrode on said insulating layer; and removing said sacrificial layer so that said driving side electrode and said insulating layer form a planarized beam.
 2. A manufacturing method of a MEMS device, comprising the steps of: forming a substrate side electrode on a substrate; forming a fluid film on said substrate side electrode and said substrate; forming a support member on said fluid film; forming a sacrificial layer on said fluid film and adjacent to said support member; forming an insulating layer on said sacrificial layer and said support member; forming a driving side electrode on said insulating layer; and removing said sacrificial layer so that said driving side electrode and said insulating layer form a planarized beam.
 3. A manufacturing method of the MEMS device according to claim 1, wherein said fluid film is a silicate glass.
 4. A manufacturing method of the MEMS device according to claim 2, wherein said fluid film is a silicate lass.
 5. (canceled)
 6. (canceled)
 7. A manufacturing method of the MEMS device according to claim 3 wherein said silicate glass film is formed of a silicon oxide film by means of a CVD method in which ozone and alkoxysilane are used as materials.
 8. A manufacturing method of the MEMS device according to claim 4, wherein said silicate glass film is formed of a silicon oxide film by means of a CVD method in which ozone and alkoxysilane are used as materials. 